lecture 11 sexual selection Flashcards
what is intra sexual selection
is when members of the same sex (within a species) compete with each other in order to gain opportunities to mate with others, e.g. the male against male competition for females
what is intersexual selection
members of one biological sex choose mates of the other sex to mate with
how does intra-sexual selection favours traits that help
individuals win competitions for matings, e.g. antlers on male red deer
the ones with better antlers for example are the better fighters and therefore get to mate so pass on the genes for the better bigger antlers
in basic terms why is being choosy adaptive
it offers evolutionary benefits if potential mates are
variable in qualities which might affect reproductive success
three catorogies of why being choosy is adaptive
right species
direct
indirect
why is getting the right species adaptive
hybrids are often sterile or ‘unfit’ in the evolutionary sense
- females in possible hybrid zones have undergone selection to be more choosy
than females in allopatric zones, e.g. Litoria frogs
why is direct adaptive
direct benfits can be gained
what direct benfits can be gained
mates may provide food (terns), parental care(great tits), nest sites, protection from other males(sheep),
what are some indirect benefits
parasite resistance longevity ‘sexiness’ ‘Good genes’… …are inherited by the offspring …increase offspring viability
what are some secondary sexual characteristics that influence
song complexity in Sedge Warblers
tail length in Long-tailed Widow Birds
what are the two hypothesis as to why secondary sexual characteristics evolved?
fishers runaway hypothesis
Zahavi’s Handicap Principle or Good Genes Hypothesis
breif exp fishers runaway hypothesis
traits can become elaborate if they co-evolve with female preference
breif exp zahavis handicap principle
or they provide an honest signal of quality
what questions must be answered to understand how secondary sexual characterisics
- How female preferences might arise
- How a preference and a trait may become genetically linked
- How this might lead to a runaway process of increase in the males’ trait
- Why males do not develop ever larger and larger traits if females would apparently prefer
them
how may female preference come about (with evidence)
sensory bias:
a louder call or larger tail may simply be spotted earlier or more noticable against the habitat (evidence: male
frogs which call as loud as possible to attract a mate because female frogs follow a simple
sound gradient when searching for a partner; a female which heads towards the loudest call
would be likely to be heading towards the nearest male.)
Arbitrary bias A bias towards a particular trait, such as tail length might exist but may be
neither costly nor beneficial until it is also linked with some selection on that trait – for
example males with slightly longer tails might be more aerodynamic in flight.
what was malte anderssons experiment on long tailed widow birds
Trapped males
Shortened some tails, lengthened others, some stayed the same as controls
results: the ones with the lengthend tails got more mates and the ones with shortened tails got less mates. the control remained the same
what was clive catchpoles study on sedge warblers
sampled different bits of the warblers song and put femles in choice chambers. the songs with the largest repitoir of song parts were favoured by the females
what is linkage disequlibrium
the non random breeding that comes from females mating with males that they find attractive; resulting in offspring that either have that feature (male) or females that find that feature desirable
why does fishers runaway process eventually stop
A trait such as tail length will vary from male to male. If females prefer the males with the longest tails, then
males will be at a mating advantage and will have a
reproductive success than short tailed males. this will continue to be a selected trait that increases over time and is stopped bt natural selection ie. if the tail gets too long it may not be able to escape predation and therefore not reproduce
what is the flow of logic of zahavis handicap priciple
1) extravagent traits are a hinderance to survival
2)only high quality individuals can actually survive with the hinderance and therefore these good genes(eg parasite resistance, food finding) will be passed onto their young. which is adaptive for females to make the choice of in the first place
3)The signal is an honest one because only genuinely healthy males will be able to produce
or survive with a large signal/trait.
4)Males are, therefore, under strong sexual selection to produce as large a signal as they can
to attract females. Again, natural selection could act as a brake on an ever increasing trait
size, but additionally the males should be unable to produce a signal which suggests they
are a better male than they really are because of the cost of producing and maintaining
such a trait.
which theory is correct
probably a mixture of both is the most likely explanation
